In many cases, transaction processing requires the use of multiple resources. Typically, each of the resources can maintain Atomic, Consistent, Isolated, and Durable (ACID) properties. A transaction manager is often used to maintain the ACID properties over multiple resources. For example, consider a single transaction involving the changing of an account balance in a database and sending of a wire transfer. It is crucial that both portions of the transaction either both occur or both do not occur. Otherwise, either the bank balance is debited without a wire transfer or the funds are transferred without debiting the bank account. Such a failure of the transaction is called a heuristic failure. If neither portions of the transaction occur, the transaction can rolled back and tried again.